In current motor vehicle cooling systems, the coolant circulates between the components to be cooled, for example the engine, the generator, etc., and the radiator, independently of the engine load, with a relatively high, thermostat-controlled temperature of approximately 100° C., in order to minimize friction losses on the engine as much as possible. If cooling water with a much lower temperature is required to cool certain components or operating media, for example, the transmission, exhaust gas recirculation, charging air, etc., its own circuit with a separate, low temperature cooler is necessary. Often the main water radiator is structurally divided and one part is used as the low temperature cooler. On the vehicle either two radiators are installed, one high temperature radiator and one low temperature radiator, which causes installation space problems, or the main water radiator is divided into a high temperature part and a low temperature part. This division leads to problems with thermal stresses and reduces the cooling efficiency that is required for actual engine cooling.
DE 196 33 190 A 1 discloses a cooling system in which an exhaust gas cooling means is integrated into an engine cooling circuit and is connected via a branch line and a return line to the lines of the engine cooling circuit. In the engine warm-up phase the exhaust gas cooling means can be decoupled from the engine, a low temperature circuit for cooling the exhaust gas cooling means being formed. Decoupling takes place depending on the temperature using a thermostatic valve. Cooling water then circulates between the exhaust gas cooling means and the engine radiator, bypassing the engine. In the branch line, which branches off from the coolant line which leads to the engine from the engine radiator, there is a circulation pump for this purpose. The return line is routed from the cooling means into a return line which leads from the engine to the engine radiator.
The object of this invention is to devise a cooling system, based on the prior art, which makes available an improved tailor-made low-temperature circuit.